Technical Field
The present disclosure relates to a method of treating a copper alloy containing metallic surface using laser ablation and application of a N2 assist gas.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Phosphor bronze finds wide applications in industry due to its good formability, desirable resistance to corrosion in marine environments, and high electrical and thermal conductivities [Z. Han, Y. F. He, H. C. Lin and H. Zhao: ‘Dealloying characterizations of Cu—Al alloy in marine environment’, J. Mater. Sci. Lett., 2000, 19, (5), 393-395.—incorporated herein by reference in its entirety]. In general copper alloys have antimicrobial attributes and several bacteria, known to be human pathogens, die when they come in contact with dry copper and copper alloy surfaces at room temperature. It has been demonstrated that the amount of live bacteria dropped several orders of magnitude, to zero in 1-2 hr when they were in contact with a copper alloy surface [G. Grass, C. Rensing and M. Solioz: ‘Metallic copper as an antimicrobial surface’, Appl. Environ. Microbiol., 2011, 77, (5), 1541-1547.—incorporated herein by reference in its entirety]. However, the use of phosphor bronze in antibacterial environments requires special attention to improve the surface properties of the alloy prior to its application in such environments. In this case, improvement of the surface hydrophobicity of the alloy reduces the contact area of bacterial fluid and minimizes the stains left over after the dry out of the hazardous fluid at the surface. However, phosphor bronze surfaces are hydrophilic and it is hard to repel the infected fluids from the surface [N. J. Shirtcliffe, G. McHale, M. I. Newton and C. C. Perry: ‘Wetting and wetting transitions on copper-based super-hydrophobic surfaces’, Langmuir, 2005, 21, (3), 937-943.—incorporated herein by reference in its entirety]. The surface hydrophobicity can be improved significantly via texturing of the surface while forming nano/micro sized poles and cavities.
One of the methods to texture the bronze surface is the laser ablation of the alloy surface in a controlled environment. In addition, laser surface treatment improves tribological properties of the surface such as hardness, wear and corrosion resistance [B. S. Yilbas, I. Toor, J. Malik, F. Patel and C. Karatas: ‘Electrochemical testing of laser treated bronze surface’, J. Alloys Compd, 2013, 563, 180-185.; and B. S. Yilbas, S. Akhtar and C. Karatas: ‘Laser nitriding of the surface of phosphor bronze’, Int. J. Adv. Manuf. Technol., 2013, 65, (9-12), 1553-1565.; and B. S. Yilbas, S. Akhtar, C, Karatas and C. Chatwin: ‘Laser embedding of TiC particles into the surface of phosphor bronze’, Surf. Interf. Anal., 2012, 44, (7), 831-836.—each incorporated herein by reference in its entirety]. Although laser treatment improves surface characteristics of bronze, the high temperature gradient generated during the process causes thermally induced cracks and limits the practical application of the treated surface. In addition, the high thermal conductivity of bronze makes the desired thermal texturing difficult to achieve. Consequently, investigation into laser treatment of phosphor bronze as it relates to surface hydrophobicity becomes essential.
Considerable research studies have been carried out to examine laser treatment of bronze surfaces. Characterization of the patina formed on a low tin bronze exposed to aqueous hydrogen sulfide was investigated [M. Chan, A. Capek, D. A. Brill and S. J. Garrett: ‘Characterization of the patina formed on a low tin bronze exposed to aqueous hydrogen sulfide’, Surf. Interf. Anal., DOI: 10?1002/sia.5520, 2014.—incorporated herein by reference in its entirety]. It was demonstrated that unlike bronzes exposed to oxidizing conditions, which developed protective SnO2 layers, the H2S (aq.) exposed surface was considerably depleted in Sn. A study on the surface properties of gilt-bronze artifacts after Nd:YAG laser cleaning was also carried out [H. Lee, N. Cho and J. Lee: ‘Study on surface properties of giltbronze artifacts, after Nd:YAG laser cleaning’, Appl. Surf. Sci., 2013, 284, 235-241.—incorporated herein by reference in its entirety]. This study demonstrated that chemical cleaning removed corrosion products of copper through dissolution; however, the removal was not uniform at the surface. Microstructure and performance of laser cladding on the surface of aluminum bronze was also studied [J.-L. Xu, B. Yang, W. Gao, Z.-P. Wang, D.-W. Long, C.-Y. Ju and T. Yu: ‘Microstructure and performance of laser cladding on surface of aluminum bronze’, J. Aeronaut. Mater., 2009, 29, (1), 63-67.—incorporated herein by reference in its entirety]. This study demonstrated that the microstructure of cladding was affected by solidification rate and a cellulated crystal microstructure was formed at the surface; however, a dendritic crystal microstructure was present in the middle section of the cladding. Laser surface alloying of a marine propeller bronze using aluminum powder has also been investigated [F. T. Cheng, C. H. Tang and H. C. Man: ‘Laser surface alloying of a marine propeller bronze using aluminium powder’, Surf Coat. Technol., 2006, 200, (8), 2594-2601.—incorporated herein by reference in its entirety]. This study showed that the difference in galvanic effect between the laser treated and as received samples was small.
Laser processing of nickel-aluminum bronze for improved surface corrosion properties has also been examined [R. Cottam, T. Barry, D. McDonald, H. Li, D. Edwards, A. Majumdar, J. Dominguez, J. Wang and M. Brandt: ‘Laser processing of nickel-aluminum bronze for improved surface corrosion properties’, J. Laser Appl., 2013, 25, (3), DOI: 10.2351/1.4799555.—incorporated herein by reference in its entirety]. The findings revealed that laser processing improved the corrosion resistance of the treated surface. Investigation of laser surface melting of a manganese-nickel-aluminum bronze has also been carried out [C. H. Tang, F. T. Cheng and H. C. Man: ‘Effect of laser surface melting on the corrosion and cavitation erosion behaviors of a manganese-nickel-aluminium bronze’, Mater. Sci. Eng. A (Struct. Mater.: Proper., Microstr. Process.), 2004, A373, (1-2), 195-203.—incorporated herein by reference in its entirety]. The study indicated that erosion-corrosion synergism constituted a significant contribution to the overall cavitation erosion-corrosion in 3-5 wt % NaCl solutions for the treated surface. Mechanical and electrochemical properties of a laser surface modified titanium alloy for biomedical applications has also been examined [M. E. Khosroshahi, M. Mahmoodi, H. Saeedinasab and M. Tahriri: ‘Evaluation of mechanical and electrochemical properties of Ti6Al4V alloy surface modified by Nd:YAG laser for biomedical applications: an in vitro study’, Surf. Eng., 2008, 209, 24-27.—incorporated herein by reference in its entirety]. The study showed that a high value of microhardness resulted from the treatment, which could be attributed to grain refinement associated with laser melting and rapid solidification.
Laser melt injection of tungsten carbide (WC) particles on an aluminum surface has also been studied [F. Q. Li, L. Q. Li and Y. B. Chen: Arc Enhanc. Laser Melt Inject. WC Partic. Al Surf., 2013, 29, (4), 296-299.—incorporated herein by reference in its entirety]. The study demonstrated that the powder should be fed from the back side of the laser beam to achieve an appropriate surface enhancement effect. Additionally, the depth of the melt layer increased initially, and then, decreased with increasing laser power. Laser processing of a TiC reinforced composite layer on an Al—Si alloy surface has been investigated as well [A. Viswanathan, D. Sastikumar, U. Kamachimudali, H. Kumar and A. K. Nath: ‘TiC reinforced composite layer formation on AlSi alloy by laser processing’, Surf. Eng., 2007, 23, (2), 123-128.—incorporated herein by reference in its entirety]. The findings revealed that the layer was free from pores and the TiC and Al—Si phases were almost uniformly distributed in the Ni—Al matrix. Laser ablation of an archaeological bronze plate surface underwater has also been investigated [B. A. Dajnowski: ‘Laser ablation cleaning of an underwater archaeological bronze spectacle plate from the H.M.S. DeBraak shipwreck’, The International Society for Optical Engineering, Vol. 8790, DOI: 101117/12?2022526, 2013.—incorporated herein by reference in its entirety]. The study indicated that laser ablation provides a clean surface of bronze plate with a minimum of damage.
Fabrication of a super hydrophobic surface on a metal via laser ablation has also been demonstrated [M. H. Kwon, H. S. Shin and C. N. Chu: ‘Fabrication of a superhydrophobic surface on metal using laser ablation and electrodeposition’, Appl. Surf. Sci., 2014, 288, 222-230.—incorporated herein by reference in its entirety]. This study showed that the spacing of the micro pillars in the array played a major role in the structure hydrophobicity that was confirmed by measuring the water contact angle. In addition, the surface morphology changed relative to the parameters of the laser ablation process. Laser ablation of metal substrates for super hydrophobic effect has also been studied [M. Tang, V. Shim, Z. Y. Pan, Y. S. Choo and M. H. Hong: ‘Laser ablation of metal substrates for super-hydrophobic effect’, J. Laser Micro Nanoeng., 2011, 6, (1), 6-9.—incorporated herein by reference in its entirety]. This study demonstrated that the pulsed laser ablation was a versatile approach for creating large area super hydrophobic surfaces for industrial applications.
In view of the forgoing, one object of the present disclosure is to provide a method of treating metallic surfaces comprising a copper alloy using laser ablation and application of a N2 assist gas.